1. Technical Field
The present invention relates to a system for controlling a robot
2. Related Art
An industrial robot is typically connected to a robot controller by a power cable and a signal cable. The power cable is used for supplying power from the robot controller to the industrial robot motor. The signal cable is used for transmitting information relating to motor speed from the industrial robot to the robot controller. The robot controller sends operation instructions to actuators of the industrial robot through these connection cables to make the industrial robot perform a desired operation.
When such a robot controller is used to control, for example, a four-axis control industrial robot, the robot controller has four servo amplifiers. When used for controlling a six-axis control industrial robot, the robot controller has six servo amplifiers. Thus, a special type of robot controller is selected for each type of industrial robot. Therefore, a special type of robot controller must be prepared for each type of industrial robot. This increases production costs.
Accordingly, the formation of a robot controller system including a plurality of robot controllers has been proposed to flexibly cope with expansions or changes in the functions of the robots.
JP-A-10-20910 describes a main controller connected to a plurality of sub-controllers. The main controller stores definition files respectively defining plural types of robots. The main controller selects the definition file of the robot type that is to be controlled and sequentially computes movements and joint angles of the robot. The sub-controllers compute the drive amounts of actuators based on the movements and joint angles computed by the main controller to drive-control the actuators. When the function of a robot is expanded or changed, the robot controller is able to cope with the expansion or change just by changing the definition file. This eliminates the need of providing additional robot controllers and enables the use of existing robot controllers.
JP-A-10-20922 describes that the main controller stores drive programs for sub-controllers. The main controller has the sub-controllers download the associated drive programs at a predetermined timing. Thus, the robot controller is able to flexibly cope with changes or updates in the drive programs.
JP-A-2000-112512 describes a plurality of robot controllers, each including a transceiver and a memory. Each of the robot controllers exchanges I/O information with other robot controllers and stores common I/O information in its memory. This exchange of information makes it possible, for example, to control a six-axis control industrial robot through cooperation between a robot controller having four motor drivers and a robot controller having two motor drivers. Accordingly, this enables the use of common robot controllers.
However, with the above robot controller system, the sub-controllers sequentially compute control commands for the associated actuators. Therefore, each sub-controller has a CPU for computing control commands and a memory serving as a working area for the CPU. As a result, the size and cost of the sub-controllers are increased. This leads to problems such as increase in installation space and cost of the robot controller system.
Moreover, in the conventional robot controller system described above, the main controller is required to synchronize the CPUs of the sub-controllers. This complicates the configuration of the main controller and increases the cost of the robot controller system.